[vsnet-grb-info 6863] GRB 081028: CrAO optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8455
SUBJECT: GRB 081028: CrAO optical observations
DATE:    08/11/01 03:04:41 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

V. Rumyantsev,  V. Biryukov (CrAO), A. Pozanenko (IKI) report on behalf of
larger GRB follow-up collaboration:

We observed the error box of  Swift GRB 081028 (Guidorzi et al.,   GCN 8421)
in R and I bands on Oct. 28, and BVRI on Oct. 29-31 with Shajn telescope of
CrAO.  The observations started on Oct. 28 00:40:56 (UT), i.e. ~16 minutes
after burst onset. We clearly detect the afterglow (Clemens   et al.,  GCN
8424, Olofsson et al.,  GCN 8425) in initial images. Preliminary photometry
of combined images of Oct. 28 based on  USNO-B1.0 0923-0196037 star  RA
(J2000) = 08:07:36.55, Dec. (J2000) = +02:18:29.4, and assuming R2=15.89
I=15.45 is following:

T0+     Filter, Exposure, mag.,     err.
(d)             (s)
0.0206  R       23x60     21.62 +/- 0.07
0.0415  I       30x60     21.32 +/- 0.09
0.0640  I       30x60     21.43 +/- 0.09
0.0865  I       30x60     21.20 +/- 0.08
0.1091  I       30x60     20.66 +/- 0.05

Our photometry confirms re-brightening of the optical afterglow (Schady &
Guidorzi, GCN 8431) with sharp rise and maximum after ~9400 s which is
consistent with the time of the brightening observed in the XRT light curve
(Guidorzi et al., GCN  8429).

A finding chart of initial combined image in R can be found at
http://grb.rssi.ru/GRB081028/